Sulfur trifluoromethyl compounds

Although the sulfur trifluoride compounds are generally useful as selective agents for conversion of carbonyl and carboxyl groups to difluoromethylene and trifluoromethyl groups, variations in reaction conditions are often necessary.7 Thus the reaction of aromatic ketones requires heating at 150°. Since the reaction with aliphatic aldehydes and ketones is exothermic, it is advan-... 

The most general and useful application of sulfur tetrafluoride is replacement of carbonyl oxygen and hydroxy groups by fluorine. The reaction has broad scope and is effective with all carbonyl and hydroxy compounds. Alcohols are converted into monofluoro derivatives 1, aldehydes, ketones and quinones into gew-difluoro compounds 2 and 3, and carboxylic acids, acid anhydrides, acid halides and amides into trifluoromethyl compounds 4. 

Esters of carboxylic acids are resistant toward sulfur tetrafluoride up to 300 °C. However, in the presence of an excess of hydrogen fluoride, they react like the acids to give trifluoromethyl compounds [187,235] In contrast, esters of highly fluorinated acids or alcohols react with sulfur tetrafluonde in a hydrogen fluoride solution under mild conditions without cleavage of the ester bond and give products of the replacement of carbonyl oxygen by fluorine a,a-difluoroethers [235, 236, 237, 238] (equations 124 and 125). 

Introduction of Three Fluorine Atoms Trifluoromethyl Compounds from Carboxylic Acids with Sulfur Tetrafluoridc... 

The synthesis of trifluoromethyl compounds from carboxylic acids using sulfur tetrafluoride... 

Sulfur tetrafluoride converts carboxylic acids, in the first reaction step, into the acyl fluorides, and in the second step into trifluoromethyl compounds. By selecting suitable reaction conditions, the acyl fluorides can be isolated. " Thus. /> ra-substituted benzoic acids react at 20 C to yield the acyl fluorides almost exclusively." Substitution of the carbonyl oxygen requires higher reaction temperatures. Similar findings have been made with a series of different cyclohcxanedicarboxylic acids. ... 

Some examples for the isolation of the desired poly(trifluoromethyl) compounds from product mixtures by chemical purification have been reported. In the reaction of benzene-1,2.3-tricarboxylic acid with sulfur tetrafluoride/hydrogen fluoride a mixture of 1.2,3-tris(tri-fluoromethyl)benzene (9). 1,1,3,3-tetrafluoro-4-(trifluoromethyl)-l,3-dihydroisobenzofuran... 

Carboxylic esters, usually methyl or ethyl esters, can be converted into trifluoromethyl compounds by reaction with sulfur tetrafluoride in the presence of an excess of hydrogen fluoride. In comparison to carboxylic acids more vigorous conditions are needed." Substitution of the ester group carbonyl oxygen is observed with fluoroalkyP or phenyl esters " of polyfluorocarboxylic acids, fluorine-containing a-oxo esters,fluorine-containing a- and j -hydroxy esters, " and furancarboxylic esters. ... 

See general procedure for the synthesis of trifluoromethyl compounds from carboxylic acids with sulfur tetrafluoride vide supra). Examples with reaction conditions are given in Table 8. 

Table 8. Trifluoromethyl Compounds from Carboxylic Esters and Sulfur Tetrafluoride/Hydrogen Fluoride...

A number of carboxylic anhydrides have been converted into trifluoromethyl compounds by treatment with sulfur tetrafluoride, usually in the presence of hydrogen fluoride. As in the case of carboxylic esters, vigorous conditions are needed. Some examples have been presented in Houbcn-Weyl, Vol. 5/3, pp 92, 93. Depending on the reaction conditions, different compounds can be isolated. In some, cyclic di- or tetrafluorinated ethers predominate. 1.253.254 Upon reaction with sulfur tetrafluoride/hydrogen fluoride, pyromellitic dianhydride, as well as pyromellitic acid (benzcnc-l,2,4,5-tetracarboxylic acid), gives a mixture of 1,2,4,5-tet-rakis(trifluoromethyl)bcnzcne, 1,1,3,3-tetrafluoro-5,6-bis( trifluoromethyl)- ,3-dihydroisoben-zofuran, and the fully fluorinated tetrahydrobenzodifuran in an 85-88 10-13.5 1-2 ratio (see formation of compounds 13-15, vide supra)d ... 

The synthesis of trifluoromethyl compounds from carboxylic acids using sulfur tetrafluoride has already been discussed in Houben-Weyl Vol. 5/3, p88. 

Treatment of thietane with chlorine, bromine,or sulfuryl chloride yields ring-opened materials. Trifluoromethyl hypofluorite gives tetravalent and hexa-valent sulfur-fluorine compounds 86 (a sulfurane) and 87 (a persulfurane) from thietane and 3-methylthietane. Ionization of 86 (R = H) at —20° to — 40°C was indicated by the collapse of the two doublets observed in the F nmr spec-... 

Scheme 2.66 Conversion of carboxylic acids to the corresponding trifluoromethyl compounds by sulfur tetrafluoride [125a, 140].

Figure 6.15 Absorption spectra of sulfur containing compounds. Top thiophenol (in heptane, ), thioxanthone (in hexane, ), thiourea (in water, ), bis(trifluoromethyl)thioketene (in isooctane, —).280 Bottom absorption ( ) and emission (—) spectra of adamantanethione in perfluoroalkane solvents.1257 The peak at the red edge of the S0—> Si transition coincides with the 0 0 band of phosphorescence and is attributed to S0—>T-i absorption...

The recent discovery of a convenient synthesis of sulfur tetrafluoride from sulfur dichloride and sodium fluoride in acetonitrile invited the application of this reagent in fluorination reactions. Hasek, Smith and Engelhardt showed that carboxylic acids and their derivatives can be converted into trifluoromethyl derivatives and that aldehydes and ketones are converted into 5 em-difluoro compounds. They also observed that the reaction was acid... 

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